don't create fileInfo structs for empty files. this saves memory.
this also avoids extra serial scan of all fileInfo, which should
make restore faster and more consistent.
Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>
* uses less memory as common prefix is only stored once
* stepping stone for simpler error callback api, which
will allow further memory footprint reduction
Signed-off-by: Igor Fedorenko <igor@ifedorenko.com>
